1. Field of the Invention
The present invention relates to an iris diaphragm mechanism.
2. Description of the Related Art
A diaphragm mechanism used in a conventional image pickup optical system is provided with a rotation axis which is a center of rotation of a diaphragm blade, and a drive shaft for driving the diaphragm blade. Moreover, a cam mechanism etc. for driving a plurality of diaphragm blades simultaneously has been used. Furthermore, a structure is such that a diaphragm blade adjacent to another diaphragm blade overlaps one by one. A structure proposed in Japanese Patent Application Laid-open Publication No. 2003-5248 is an example of such structure.
The structure proposed in Japanese Patent Application Laid-open Publication No. 2003-5248 includes a fixed member in which a fixed aperture is formed, and a plurality of diaphragm blades which are opened and closed pivotably with fixed shafts disposed in plurality around the fixed aperture. Moreover, at least a part of the diaphragm blades are provided with an extension shaped portion for maintaining an order of overlapping in an optical axis direction, with the other diaphragm blade. Accordingly, a shape is let to be such that a front-end portion of the diaphragm blade does not overlap with another diaphragm blade at a completely closed position.
When a structure in which the diaphragm blades overlap one after the other as in the conventional technology is adopted, with narrowing of the diaphragm blades, it is required to be deformed such that the diaphragm blade is bent. Therefore, a force which drives the drive shaft is increased.
In a diaphragm mechanism of comparatively large equipments such as a camera and a projector, an amount of bending of the diaphragm blade is also small. Moreover, an actuator having a substantial generative force can be used as an actuator for moving the drive shaft. Therefore, an increase in a force which moves such drive shaft has never been a problem.
However, from here onward, in a diaphragm mechanism which is used in a portable camera and extremely small image pickup equipment in which an application of a diaphragm mechanism is expected, it is necessary to make the diaphragm mechanism small. Moreover, in a portable camera and extremely small image pickup equipment, an actuator for driving the drive shaft is restricted to be a very small size actuator.
Whereas, from a point of a light shielding capacity, a thickness of certain degree has to be secured for the diaphragm blade. For this, in small size image pickup equipment, an amount of distortion at the time of bending the diaphragm blade is increased extremely. When the amount of distortion of the diaphragm blade increases, a frictional force of the diaphragm blades also increases.
In a small actuator which is used in the small size image pickup equipment, it is difficult to generate a substantial driving force. Consequently, an increase in a force which moves the drive shaft of the diaphragm blades with a substantial amount of distortion exerts a substantial load on a small size actuator. Moreover, when the amount of distortion of the diaphragm blade is increased, a damage caused to the diaphragm blade is also substantial.